Report of Investigations No. 123 Petroleum Potential of the Palo Duro Basin, Texas Panhandle

The Palo Duro Basin seemingly has all the elements necessary for hydrocarbon generation and accumulation: reservoirs, traps, source rocks, and sufficient thermal maturity. Porous facies in pre-Pennsylvanian, Pennsylvanian, and Permian strata are potential hydrocarbon reservoirs. Within the pre-Pennsylvanian section, shallow-marine carbonates of both Ordovician (Ellenburger Group) and Mississippian age have sufficient porosity and permeability for hydrocarbon accumulation. Three main exploration targets of Pennsylvanian and Wolfcampian age are (1) granite-wash sandstones, (2) shelf-margin carbonates, and (3) elongate-delta sandstones. Granite wash was deposited in fan deltas adjacent to fault-bounded, basement uplifts around the basin margins. Porous facies are braided-channel, fan-plain, and distal-fan deposits. Porous carbonates developed through time along the different positions of the shelf margins. Organic-rich basinal shales are juxtaposed against the porous shelf-margin facies. High-constructive, elongate-delta deposits in the southeastern part of the basin retain high porosity in bar-finger (channel-mouth bar) sandstones. In younger strata, dolomites in the Clear Fork (Leonardian) and the San Andres (Guadalupian) Formations are reservoirs along the Matador Arch. However, porosity in these units apparently pinches out to the north.

Both stratigraphic and structural traps occur in the basin. Porosity pinch-outs form the primary stratigraphic traps. Major faults are associated with the Amarillo Uplift; smaller faults have been identified in the deeper parts of the basin. Most faults are thought to have existed before the Pennsylvanian and to have been reactivated by a northwest maximum principal compression. Fracturing adjacent to some faults may have created fractured reservoirs.

The Palo Duro Basin contains source rocks of sufficient quality to generate hydrocarbons. Pennsylvanian and Wolfcampian shales contain up to 2.4 percent total organic carbon (TOC) and are fair to very good source rocks. Lipid-rich organic matter occurs primarily in basinal shales. Kerogen color and vitrinite reflectance, which measure thermal maturity, indicate that temperatures were sufficiently high to begin to generate hydrocarbons from lipid-rich organic matter. Pennsylvanian and Wolfcampian kerogen is yellow orange to orange. Average reflectance in Pennsylvanian vitrinite is 0.52 percent; in Wolfcampian samples the average reflectance is 0.48 percent. Recent oil discoveries in the Palo Duro Basin confirm that oil was generated.